DE3605635A1 - DEVICE FOR LIMITING THE MAXIMUM RADIATION INTENSITY - Google Patents

Description

The invention relates to a device for limitation the maximum radiation intensity of a radiation source, in particular a laser, and a device device for coupling in high radiation intensities ner radiation source, in particular a pulse laser, into an optical fiber.

To limit the radiation intensity of radiation sources are e.g. Gray filter with different, each known firm transparencies. Furthermore, at Glasses known as self-tinting glasses, the trans parity with increasing intensity of sunlight tes reduced.

The known devices are not suitable for Radiation intensity of a radiation source on a be limit the right maximum, underlying integers but let pass through unhindered. Also react Ren such facilities too slow on Inten sity peaks, so that especially when using damage from lasers as a radiation source occur due to excessive intensity. In particular those with pulse lasers can have such intensity increases due to spatial (hot spots) and temporal mo Dulations of the laser pulse arise.

It is therefore an object of the invention to provide a device for Limiting the maximum radiation intensity of a Radiation source, in particular a laser which, similar to electrical fuses, quickly and reacts reliably, and thus from the beam illuminated or irradiated parts  casually protects high radiation intensities and thus also the coupling of higher average radiation inks in optical devices such as Light guide enables.

This task is characterized by one after the Features of claim 1 or patent Proverb 2 trained device solved.

The invention makes use of the knowledge that in the focus of a focused laser beam when material-specific energy densities are exceeded by multiphoton absorption and cascade ionization, a plasma is formed which the laser beam can no longer penetrate (see dissertation by Dipl.Phys Jürgen Munschau "Theoretical and Experimental Un studies on the generation, propagation and application of laser-induced shock waves ", TU Berlin 1981, pages 46ff). This process is referred to as the breakdown effect, the so-called breakdown threshold value, i.e. the value of the radiation intensity at which the plasma formation begins, being dependent on the irradiated medium. This breakdown threshold is, for example, about 2 × 10 ¹⁴ W / m ² for air under atmospheric pressure and 6.4 × 10 ¹³ W / m ² for distilled water. The breakdown effect was examined in the aforementioned dissertation in connection with the generation of shock waves; technical applications beyond this are not mentioned.

Such a through can be particularly advantageous break distance with defined breakdown threshold Protection of optical fibers when coupling high Use radiation intensities. Especially with the Laser pulses occur with the use of pulse lasers  Peak intensities above that of destruction threshold of the light guide material may lie. Here due to material damage, especially in the Area of the coupling side of the light guide. Especially in the cases in which the laser light as a tool for Material or fabric processing is intended to interfere such intensity peaks especially since they are the radiated total intensity is not insignificant can increase.

When using gases as a breakdown medium can the breakdown threshold in an advantageous manner the gas pressure can be adjusted.

For coupling high radiation intensities into one Optical fiber continues to be special Proven if the radiation is not as before usual, focused, but diverging into the light conductive fiber is coupled. The easiest way to do this Trap one in front of the face of the light diverging lens arranged by a fiber or by a concave entrance face of the light guide fiber. As an opening angle for that has rays entering the optical fiber a minimum of 8 ° was found. Through this Measure is taken when using pulse lasers Pulse energy distributed over several modes, whereby lo kale intensities and self-focusing un be suppressed. With this measure the Zer interference threshold of the optical fiber raised, so that in connection with an upstream through fracture path a higher average radiation intensity and thus radiation power through the optical fiber can be directed. Such a measure can ever but also regardless of the use of a through  break line are used.

In the following the invention is based on three parts schematically illustrated embodiments be wrote.

Show it

Fig. 1 shows a device for limiting the maximum radiation intensity te protection of optical Gerä;

FIG. 2 shows a device according to FIG. 1 with an indirectly acting breakthrough distance;

Fig. 3 shows a device for coupling high radiation intensities in an optical fiber.

In the exemplary embodiment shown in FIG. 1, the parallel light beam 1.1 from a laser 2 is focused on a breakthrough path 4 by means of a focusing lens 3 , the emerging beam bundle 1.2 being coupled into any optical component 6 , which is therefore not shown, by means of further optics 5 which should be protected from exceeding a maximum radiation intensity. The breakthrough section 4 consists of a highly transparent material for the spectral range of the laser, which can be both a solid and a liquid or a gas. The breakdown threshold value, i.e. the value of the radiation intensity, at which plasma formation suddenly begins and the breakthrough distance for the laser light becomes impermeable, is material-dependent and can be influenced particularly easily by gases due to pressure changes. When using gases, it is also advantageous that the break-through section regenerates again very quickly after a breakdown and thus becomes transparent again. By a suitable choice of the focal length of the focusing lens 3 and the material used for the breakthrough distance, the switching threshold is variable over a wide range. Further information on this, in particular on the influence of optics, can be found in the above dissertation. Since the damage thresholds of optical materials are in the range of a few 10 ¹³ W / m ² , methanol, glycerine, distilled water and air as breakthrough material can already be used to protect optical components from excessive radiation intensities with the materials examined in the above thesis . Due to the high switching speed in the nanosecond range, harmful power peaks can be filtered out from pulse lasers with one of the devices, so that the average intensity of the individual laser pulses can be chosen much higher than was previously possible without the subsequent laser beam arranged optical component to destroy by too intense laser pulses. The life of such protected optical components is drastically increased.

Fig. 2 shows another embodiment showing a device for protection of optical components against inadmissible high radiation intensities, a small fraction of the radiation energy coupled in by means of a beam splitter 7 a pulse laser 8 and stretch in a breakthrough by means of a focusing lens 9 is passed 10th The breakdown threshold value of this breakthrough distance 10 is matched to the decoupled portion of the total radiation energy of the laser 8 . An optical breakthrough is registered by means of an optical or electrical detector 11 , and a radiation switch 12 is controlled with a corresponding electrical signal. The beam switch 12 is arranged between an optical delay line 13 connected downstream of the beam splitter 7 and the optical component 14 to be protected and can be constructed, for example, on an electromagnetic or electro-optical basis, for example as a Kerr or a liquid crystal cell. The advantage of this exemplary embodiment compared to that shown in FIG. 1 is that no manipulations on the laser beam influencing the beam parameters of the laser (eg phase front) have to be carried out.

FIG. 3 shows a device for coupling high radiation intensities in an optical fiber. The radiation from a laser 15 is kissed by a fo kussierlinse 16 on a breakthrough distance 17 fo, the emerging radiation is coupled via a diverging lens 18 into the optical fiber 19 . The breakthrough path 17 corresponds to the embodiments described in FIGS. 1 and 2 and shields the optical fiber from intensity peaks which lie above the destruction threshold of the optical fiber material. The diverging lens 18 distributes the radiation energy over several modes, thereby suppressing local intensity increases and self-focusing . The diverging lens 18 is located directly on the coupling face of the optical fiber and is designed so that the radiation beam entering the optical fiber has an opening angle of at least 8 °. The maximum widening of the radiation beam to be coupled in depends on the acceptance angle of the optical fiber. To reduce Reflexionsver losses, the space between the diverting lens 18 and the optical fiber 19 can be glued in a known manner or filled with a so-called index matching liquid.

The function of the diverging lens 18 can also be taken over by a correspondingly concavely ground or etched end face of the optical fiber.

Claims (8)

1. A device for limiting the maximum radiation intensity of a radiation source, in particular a laser, characterized in that a transparent breakdown path ( 4 , 10 , 17 ) with a defined breakdown threshold value is arranged within the beam path of the radiation source ( 2 , 8 , 15 ). 2. Device for coupling high radiation intensities of a radiation source, in particular a pulse laser, in an optical fiber, characterized in that a breakthrough path ( 17 ) is arranged between the radiation source ( 15 ) and the optical fiber ( 19 ), the breakdown threshold is below the destruction threshold of the optical fiber ( 19 ). 3. Device according to claim 2, characterized in that the optical fiber ( 19 ) is arranged in a divergent beam path of the radiation source ( 15 ). 4. Device according to claim 3, characterized in that the opening angle of the entering into the optical fiber ( 19 ) diverging beam is at least 8 °. 5. Device according to claim 3 or 4, characterized characterized in that the optical fiber has a concave entrance face. 6. Device according to one of claims 1 to 5, characterized in that the breakthrough section ( 4 , 10 , 17 ) contains a gas and that the gas pressure is adjustable. 7. Device according to one of claims 1 to 6, characterized in that the radiation is focused on a point within the breakthrough distance ( 4 , 10 , 17 ). 8. Device according to one of claims 1 to 7, characterized in that in the beam path of the radiation source ( 8 ) a Strahlentei ler ( 7 ) is arranged, which derives part of the radiation on a breakthrough path ( 10 ) and that in front of the beam path and / or a beam switch ( 12 ) controlled by the breakthrough path ( 10 ) is arranged behind the beam splitter ( 7 ).